Radio receiving system



1931. D. T. slmofibs 1,829,965

RADIO RECEIVING SYSTEM Filed 001;. 8, 1925 I Inventor: Dewey T Simonds;

His Atnorneg Patented Nov. 3, 1931 UNITED STATES PATENT? OFFICE DEWEY T. 8111011138, 01''' SGEENEGTA'DY, NEW YORK, ASBIGNOR '10 GENERAL ELECTRIC COMPANY, CORPORATION OF NEW YORK RADIO RECEIVING SYS'lm Application filed October 8, 1925. Serial K0. 61,853.

My present invention relates to radio receiving systems, and more particularly to systemsof te superheterodyne type.

In the superheterodyne system of recep- 5 tion a local source of oscillations is provided for producing, in combination with the received signals, beats having a frequency above audibility. lhe beat current thus produced is detected and amplified and after amplificato tion the resulting current of intermediate frequency above audibility is detected to render the transmitted signals intelligible. In practice this intermediate frequency has usually been fixed at 40,000 to 60,000 cycles. If the E6) receiving set is designed to cover a considerable range of wave length'such, for example, as the range used for broadcasting, astation can be heard with two diderent settings of the oscillator frequency. While in some cases '20) this is an advantage in that it assists in avoiding interfering stations, it also is a d1sadvantage in that the person manipulat ng the set sometimes finds it dificult to ident1fy the station which is being received.

5 When the local source of oscillations is combined directly with the current received upon the receiving loop or antenna it is also pos-' sible to produce a radiation which interferes with reception on sets in the neighborhood of the superheterodyne set. That 1s, durmg the adjustment of the osc1llator frequency, the frequency of the oscillations produced may at times be the same as that for wh ch the 100 or antenna is tuned so that appreclable ra iation will be effected.

The object of my invention 1s to overcome the disadvantages pointed out and provide a superheterodyne receiving set in which a station can be heard at only one settlng of the oscillator frequency and one in which it w1ll be substantially impossible to produce any appreciable radiation from the receiving loop or antenna. I

In carrying my inventlon into effect so proportion the circuits that the intermediate frequency produced Wlll be substantlally half of the frequency range over which the set will be efiective in reception. I also provide means for simultaneously effecting the tun- 50 ing of the receiving loop or antenna and the circuit which determines the frequency of the local oscillations so that the frequencyof the local oscillations produced will always differ from the resonant frequency of the loop or antenna by a value equal to the intermediate frequency.

The novel features which I believe to be characteristic of my invention are set forth in the appended claims. The invention itself, however, both as to its organization and method of operation will best be understood by reference to the following description taken in connection with the accompanying drawing in which I have indicated dlagrammatically a circuit organization which may be employed in carrying my invention into efl'ect.

I have indicated in the drawing a receiving sysmm comprising an oscillator tube 1, a detector tube 2, intermediate amplifying tubes 3 and 4:, a second detector tube 5 and audio amplifying tube 6. The receiving loop 7 is tuned by means of a variable condenser 8 and the oscillating circuit of oscillating tube 1 is tuned by a variable condenser 9. The signals received upon the receiving loo 7' are impressed upon the grid circuit of etector tube 2 through a potentiometer 10 for controlling the volume of the signals. The local oscillations are also impressed upon the grid circuit of the detector tube 2 by means of a variable coupling 11. The'condensers 8 and 9 may be mounted upon the same shaft or connected in other ways so that they may both be adjusted simultaneously by means of a single knob. These condensers should have what is known as a straight line frequency characteristic so that a change in the resonant frequency in one of the circuits may be accompanied by an equal change in the resonant frequency of the other circuit over the entire range of the condensers.

The output circuits of tubes 2, 3 and 4: are tuned to the intermediate frequency by means of fixed condensers 12, 13 and 14. The input circuits of tubes 3, 4 and 5 are similarly tuned by means of fixed condensers 15, 16 and 17. To prevent the generation of 0scillations of the intermediate frequency the output circuits of tubes 3 and 4 are brought to an intermediate point in the coupling :00

transformer rimaries 18 and 19, and non tralizing con ensers 20 and 21 are connected from one terminal of these transformer windings to the grids of tubes 3 and 4 for neutralizing the effect of the feed-back from the late to the grid of these tubes.

If the receiver is intended for broadcast reception, the circuit of the receiving loop 7 should be proportioned so that it may be adjusted to cover the broadcasting range extending from substantially 500,000 to 1,100,000 cycles. The circuit of the local oscillator then will be proportioned to have an effective frequency range of from 800,000 cycles to 1,400,000 cycles. The intermediate frequency roduced then will be equal to the 7 local oscil ator frequency minus the signal frequency or 300,000 cycles. It will of course be understood that the frequency range of the local source of oscillations might equally well be 200,000 to 800,000 cycles. Since the two tuning condensers are adjusted simultaneously the frequency of the local oscillations will always differ by 300,000 cycles from that of the receiving loop and hence no radiation from the loop will be produced to interfere with adjacent receivers.

Even if the condensers were not arranged to be operated simultaneously, the frequencies chosen are such that the intermediate frequency by which the set is selective can be produced at only one setting of .the oscillator. Hence a station can be heard only at one setting of the oscillator.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. The combination in a radio receiving set, of a resonant receiving circuit having an effective frequency range of 500,000 to 1,100,000 cycles, a local source of oscillations, means for combinin oscillations from said local source with oscillations received in said receiving circuit to produce beat currents of substant1ally 300,000 cycles, said source of oscillations having an effective frequency range such that said heat currents are produced throughout the effective frequency range of the receiving circuit, and means including a circuit tuned to said last named frequency for amplifying and detecting the beat currents thus produced.

2. The combination in a radio receiving set, of a resonant receivin circuit having a predetermined efi'ective i requency range, an intermediate frequency amplifier responsive to a frequency substantiall equal to one-half the difference between t e limiting values of said frequency range, a local source of oscillations having an efl'ective frequency range such that when combined with oscillations received in said receiving circuit at any point in the effective tuning range thereof said oscillations produce heat current of the frequency to which the intermediate frequency amplifier is responsive, means for combinin oscillations from said local source with osci ations received in said receiving circuit to produce beat currents of said intermediate frequency, and means connected with said intermediate frequency and lifier for detecting the beat currents thus pro uced.

3. The combination in a radio receiving set. of a receiving circuit, a tuning means for adjusting the resonant frequency of that circuit over a predetermined frequency range, a local source of high frequency oscillations, tuning means for adjusting the frequency of said source over a frequency range of substantially the same amount and having a lower limit which differs from the corresponding limit of the receiving circuit by an amount substantially equal to half the frequency range of the receiving circuit whereby beat currents of such intermediate frequency are roduced, an intermediate frequency amplifier tuned to said frequency for amplifying said beat currents, and means for simultaneously adjusting the tuning means of the receiving circuit and of the local source.

4. The combination in a radio receiving system of a resonant receiving circuit having a predetermined effective frequency range, a local source of oscillations having an effective frequency range of substantially the same amount, a second resonant circuit having a fixed tuning and means for combining oscillations from said local source with signaling oscillations received in said receiving circuit and supplying beat currents to said second resonant circult, the fre uency of said second circuit being so fixed t at with substantially any signaling frequency within the effective range of the receiving circuit beat currents of the fixed frequency can only be produced with one frequency within the effective range of the local source.

5. In a superheterodyne receiver, the combination with an oscillator and a tuned receiving circuit, of means for preventing the oscillator from beating within the range of frequencies to be received at more than one tunlng point throughout the range of the oscillator frequencies, said means including an intermediate frequency amplifier tuned to a frequency of an amount substantially equal to half of the tunin range of said receiving circuit, and means or tuning the oscillator to produce a beat current at said frequency throughout the tuning range of said receiving circuit.

6. In a superheterodyne receiver, the com bination with an oscillator and a receiving circuit provided with a tuning means, of means for preventing the oscillator from beating within the range of frequencies to be received at more than one tuning point throughout the range of the oscillator freapencies, said means including an intermeate frequency amplifier tuned to a he quency of an amount substantially equal to half of the tuning range of said receiving c1rcuit, means for tuning the oscillator to produce a beat current at said frequency 5 throughout the tuning range of said receiving circuit, and means for operating the tuning means for said receiving circuit and for said oscillator simultaneously and in a fixed spaced tuning relation to each other for prom ducing said beat currents whereby said oscillator and said receiving circuit are prevented from being tuned simultaneously to the same frequency and from effecting radiation at such frequency.

7. In a superheterodyne receiver, the combination of a tuned receiving circuit, said circuit being variably tunable over a range of frequencies to be received, an intermediate frequency amplifier having tuned cir- 0 cuits responsive to a frequency of an amount substantially equal to one-half of the tuning range of said receiving circuit, an oscillator coupled to said receiving circuit and tunable over a range of frequencies for producing beat currents at the frequency to which said amplifier is responsive throughout the tuning range of said receiving circuit, and means for applying said beat currents to said intermediate frequency amplifier.

no 8. In the method of receiving radio signals within a given range of frequencies by the superheterodyne method in which the signal frequency is made to produce an intermediate difference frequency by beating 85 with local oscillations, the step of producing an intermediate difference frequency so high that it can be produced by only one signal frequency within the said range.

' 9. The method of radio reception which 40 comprises, producing an intermediate difference frequency between an incoming signal of a predetermined range of frequencies and local oscillations, said signal frequency having an image frequency which differs from the frequency of said local oscillations by an amount equal to the difference between said signal frequency and said. local oscillations, said image frequency being greater than said predetermined range of frequencies.

10. The method of radio reception which comprises, producing an intermediate difference frequency between an incoming signal of a predetermined range of frequencies and local oscillations, said signal frequency having an image frequency which differs from said local oscillations by an amount equal to the intermediate frequency and said image frequency lying outside of said predetermined range.

In witness whereof, I have hereunto set my hand this 7th day of October, 1925.

' EWEY T. SIMONDS. 

